A. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an in-plane switching ("IPS") mode liquid crystal display device.
B. Description of the Related Art
Recently, the thin film transistor liquid crystal display devices (TFT LCDs) have been used as display devices in such applications as portable televisions and notebook computers, but these TFT LCDs have small viewing angles.
In order to solve this problem, twisted nematic LCDs having, for example, optical compensation films and multi-domains, have been introduced. In these LCDs, however, the color of the image is largely shifted as the viewing angle direction increases.
For a wide viewing angle, the IPS mode LCD is disclosed, for example, in JAPAN DISPLAY 92 page 547, Japanese Patent Unexamined Publication No. 7-36058, Japanese Patent Unexamined Publication No. 7-225388, and ASIA DISPLAY 95 page 707.
FIG. 1 is a view showing the operation of liquid crystal (LC) molecules of the conventional IPS mode LCD. FIG. 2 is a view showing the long axis of the LC molecules shown in FIG. 1. As shown in the figures, a data electrode 8 and a common electrode 9 are aligned in Y axis direction at an angle .theta..sub.EL =90.degree. relative to the X axis direction which is the extension direction of a gate bus line (not shown). .theta..sub.E =180.degree. indicates an angle between the direction of electric field and X axis direction. .theta..sub.R indicates an angle between the alignment direction and the X axis direction, and angle .theta..sub.R is determined by a rubbing process in the range of 90.degree. to 180.degree.. .theta..sub.rot indicates a rotated angle of liquid crystal molecules 35 by the electric field applied between the two electrodes.
When a voltage is not applied, liquid crystal molecules 35 denoted by dotted line are aligned according to the alignment direction at angle .theta..sub.R. When the voltage is applied, liquid crystal molecules 35 rotate counterclockwise by angle .theta..sub.rot. In the figures, liquid crystal molecules 35 are denoted by solid line after the voltage is applied, and a positive type liquid crystal is used in which electric permittivity of liquid crystal molecules in the long axis direction is larger than in the short axis direction. On the other hand, when negative type liquid crystal is used, the liquid crystal molecules are aligned perpendicular to the electric field direction.
However, in the conventional IPS mode LCD, grey level inversion is caused by birefringence of the liquid crystal molecules as shown in FIG. 3a. Further, as shown in FIG. 3b, a white color is shifted to blue and yellow colors respectively in A and B viewing directions shown in FIG. 1.